Abstract
This paper presents the design and experimental characterization of a portable high-precision single-phase lock-in instrument with phase adjustment. The core consists of an analog lock-in amplifier IC prototype, integrated in 0.18 µm CMOS technology with 1.8 V supply, which features programmable gain and operating frequency, resulting in a versatile on-chip solution with power consumption below 834 µW. It incorporates automatic phase alignment of the input and reference signals, performed through both a fixed −90° and a 4-bit digitally programmable phase shifter, specifically designed using commercially available components to operate at 1 kHz frequency. The system is driven by an Arduino YUN board, thus overall conforming a low-cost autonomous signal recovery instrument to determine, in real time, the electrical equivalent of resistive and capacitive sensors with a sensitivity of 16.3 µV/Ω @ εrS < 3% and 37 kV/F @ εrS < 5%, respectively.
Highlights
Device miniaturization has been key to the development of innovative sensing technology with application in different fields [1], ranging from biology and medicine [2,3], to environmental monitoring [4,5,6], or limnology and civil structural monitoring [7,8,9]
A lock-in amplifier (LIA) is based on phase-sensitive detection (PSD), where the signal of interest (VIN, f 0 ) is multiplied by a reference signal (VR ) whose frequency is set at f 0 to perform a synchronous detection; the resulting signal is low-pass filtered with a Electronics 2019, 8, 1413; doi:10.3390/electronics8121413
As the system presents the maximum sensitivity for the in-phase condition (θ = 0◦ ), single phase lock-in amplifiers work with input and reference signals operating at the same frequency and in phase
Summary
Device miniaturization has been key to the development of innovative sensing technology with application in different fields [1], ranging from biology and medicine [2,3], to environmental monitoring [4,5,6], or limnology and civil structural monitoring [7,8,9]. This paper addresses the implementation of such an instrumentation board, based on an analog integrated lock-in amplifier [19] that exhibits low power consumption, flexibility due to its programmable gain and operating frequency and small size and compared to state-of-art LIAs, being a very competitive choice in terms of large scale reproducibility [4,5,24], with an automatic signal synchronization system driven by an Arduino YUN board which manages all the measurement process and that acts as an intuitive interface between the processing system and the data storage in the PC [25].
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